coating challenges for fasteners in defense and aerospace€¦ · coating challenges for fasteners...

Keith Legg 847‐680‐9420 [email protected]://www.asetsdefense.org Teaming website: www.materialoptions.com

Coating Challenges for Fasteners in Defense and Aerospace

Keith Legg

ASETSDefense

Rowan Technology Group

Libertyville, IL

FastenerTech 6/2009


Tout se change, tout c’est la même chose

Pressure from a variety of environmental and health rules in the US and overseas is driving adoption of new (and often better) coatings for fasteners

Changes since FastenerTech ‘07New DoD memo to eliminate Cr6+ from new equipment

REACH impact becoming clearer

Army looking to replace Cd‐plated fasteners on vehicles

Several new projects on fasteners


Standard military and aerospace fasteners

Why Cd?

Cheap and easy

Sacrificial, but not too electronegative so lasts a long time

Low volume of corrosion productsInhibits “freezing”

Not electrically insulating

Lubricious, reliable torque‐tension

No re‐embrittlement

No fatigue debit

steel

cadmiumchromate conversion


Drivers for change


Changing materials

Materials are changing, especially in defense and aerospace

Composites (carbon fiber, glass fiber)u Insulating organic matrix, conducting carbon fibers

High use of Al, increasing use of stainless steel, Ti, Mgu A lot of potential for galvanic corrosion

u Potentially puts Al, steel, C in galvanic contact

Al airframeshim

C-fiber composite

fastener


DoD Memo on Cr6+

April 8 ‘09 OSD issued memo restricting Cr6+

use, unless no cost‐effective alternatives with satisfactory performance

Requires Program Executive Officer (PEO) and Corrosion Control and Prevention Executive (CCPE) to certify if no acceptable alternative


Changing environmental and health requirements

The wars of the RoHSesEuropean RoHS, China RoHS, CA RoHS

Severely restricting Cd, chromates on electrical equipment sold in EU – aerospace and defense exempt

US RoHS, HR 2420 “Environmental Design of Electrical Equipment Act (EDEE) Act”

Hath not thy RoHS a thorn?

http://www.mediageek.ca/arsenicjade/home.html


Meeting the RoHS rules

Companies selling electrical equipment and vehicles in the EU must certify RoHS compliance

With HR 2420 we will have the same here

For many companies the biggest difficulty with meeting the RoHS requirements is with fasteners because they have no control over them

What works depends on the environment in which they will be used

No homogeneous layer can contain >0.1% Cr6+

or >0.01% Cd by weight“Homogeneous layer” means any layer that cannot in principle be mechanically disjointedThe chromate layer is a homogeneous layer, not the chromated Zn or Cd

Zn or Cd <0.01wt% Cd<0.1wt% Cr6+

<0.1wt% Cr6+


What about REACH?

Cr6+ not affected by REACH at this timeSodium dichromate was put forward in first Annex XIV group, but decided not to make it a priority substance at this time

Cd plating permitted on aircraft and some other applications, but otherwise severely restricted

Not permitted on vehicles, and military vehicles do not seem to be exempt

Most US military vehicles in Europe use Cd‐plated, chromated fasteners


But aren’t we exempt?

Military and aerospace are exempt (for now) from WEEE and RoHS but not from OSHA or EPA

HR 2420 does not have aerospace or defense exemptionUnlikely to stay that way

No defense exemptions built into REACHUK has Defense Exemption, but does not exempt from rules, only from disclosures to ECHAOther EU countries considering similar laws

Being exempt from REACH or RoHS does not make us exempt from their effects. Military and aerospace users are concerned about

Reduced availability of chromated materialsReduced availability of Cd platingHigher prices, longer lead timesSelling and maintaining equipment in Europe


Personnel safety

All military systems and aircraft need paint touch‐up for corrosion control and aestheticsWhen scuff sanding, Cd plated, chromated fasteners and chromate converted Al with chromate primers are a serious personnel hazard

Especially bad for uncontrolled areas – flight lines, forward bases, etc.Even in factories and military depots, sanding for touch‐up or bonding creates chromate dustNew OSHA Cr6+ rules require keeping unprotected workers away from site generating Cr6+ dust

o Makes these operations very inefficient and disruptive


Result

DoD and aerospace companies are looking for good alternatives to Cd-plated, chromate converted fastenersElectrical equipment makers want chromate-free fasteners


Where do military fasteners come from?

OEMs if they are special design

Defense Logistics AgencyMost standard fasteners bought by DLA

Military users then purchase from DLA

But DLA will only stock if there is a demando Catch‐22

Fasteners must make it onto QPL (Qualified Products List)o Must meet user requirements and pass qualification testing

Users must be convinced new fasteners will work as well as (preferably better than) existing products


Military and aerospace requirements for non‐Cd fasteners

Corrosion performance at least as good as Cd

Sacrificial protection ‐ A barrier can always be breached

No hydrogen embrittlement (high strength alloys)Either not embrittle or can be baked out

No environmental embrittlement (re‐embrittlement) in typical operational and overhaul fluids

Sacrificial coating must not dump H into substrate

No fatigue debit

Acceptable primer adhesion

For aircraft must be lighting‐strike proof

Reliable torque‐tension, breakaway torqueLooks as though can achieve this through Dry Lubes

Enormous cost of changing repair manuals if torque changes


Barriers to change

Performance qualificationExisting technical data on relevant tests

Additional testing required for qualification

Buy‐in from different DoD program managers in different services

Change costs for drawings and contractsData Conversion Laboratory has estimated that converting all the manuals for one aircraft carrier alone to CD-ROM would lighten the ship so much it would sit 3 inches higher in the water.


Moves afoot to develop DoD alternatives

Army TARDEC hopes to change to AlumiPlated fasteners with permanent polymer lubricant to be available through DLA

Idea is a single solution to avoid confusion

Several SERDP projects to develop/evaluate fastener coatings (http://www.serdp.org/research/WP‐Heavy‐Metal‐Elimination.cfm )

Luna Innovations – vacuum‐deposited ZnNiCo

Akzo Nobel – CVD Al

Integran – pulse plated ZnNi

PPG – dip spin metal filled polymer basecoat + electrocoat topcoat

http://www.serdp.org/research/WP-Heavy-Metal-Elimination.cfm

http://www.serdp.org/research/WP-Heavy-Metal-Elimination.cfm


What works?


Aerospace

In engines most fasteners are now corrosion resistant (CRES) alloys such as stainless steels and high strength Ni alloys such as Waspaloys

Fits very well with other engine alloys (Inconels, etc)

Not an option for Al aircraft skins and airframesSerious galvanic corrosion problem

When used with Al or Mg both high strength and stainless steels are Cd plated

Good options for aircraft airframes areAl coatings – IVD or electroplate

ZnNi electroplates


Getting the Cr6+ off Zn

There are a great many Cr3+ and non‐Cr passivates for Zn and Al

Workshop held in Layton, Utah, 2007 to explore chromate alternatives

Workshop report available:http://www.asetsdefense.org/PastWorkshops.aspx

http://www.asetsdefense.org/PastWorkshops.aspx


NEW SOURCE OF INFORMATION


ASETSDefensehttp://www.asetsdefense.org

Quick information on alternatives

ASETSDefense workshop agendas, briefings, summaries(HCAT meetings coming soon)

Database

Team Work Spaces

Tools to be added

http://www.asetsdefense.org/

http://www.google.com/imgres?imgurl=http://www.ensureslm.co.uk/images/mouseiconlarge_pointer.gif&imgrefurl=http://www.ensureslm.co.uk/&h=265&w=192&sz=5&tbnid=07GPyrFPF-T70M:&tbnh=112&tbnw=81&prev=/images?q=pointer+icon&usg=__izaN54KXlHQ7d7_FS1oF1ajVDio=&ei=AG8hStenMYHCM7mx2KIJ&sa=X&oi=image_result&resnum=3&ct=image


Quick Links basic information


Database

What is there so far

Click to search

No passwordneeded

for most data

http://www.google.com/imgres?imgurl=http://www.ensureslm.co.uk/images/mouseiconlarge_pointer.gif&imgrefurl=http://www.ensureslm.co.uk/&h=265&w=192&sz=5&tbnid=07GPyrFPF-T70M:&tbnh=112&tbnw=81&prev=/images?q=pointer+icon&usg=__izaN54KXlHQ7d7_FS1oF1ajVDio=&ei=AG8hStenMYHCM7mx2KIJ&sa=X&oi=image_result&resnum=3&ct=image


Detail search

Search for specific materials, systems, tests, people, organizations

corrosion

Looking for info on what approvals and specs exist for Cd and Cr6+

alternatives and where they are being used


ASETSDefense ’09Coming in September

ASETSDefense ’09: Sustainable Surface Engineering for Aerospace and Defense

Denver, September 1‐3, 2009

Aircraft, ships, vehicles

Alternatives to chromate primers, sealers, conversion coats, low VOC paint systems, hard chrome, Cd plate

Stackups, hydraulics, fasteners, electrical connectors

coating challenges for fasteners in defense and aerospace€¦ · coating challenges for fasteners...

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